A COMPARATIVE-STUDY OF VOIDING IN RAT AND GUINEA-PIG - SIMULTANEOUS MEASUREMENT OF FLOW-RATE AND PRESSURE

In this study, the voiding phase of the micturition cycle in the anest hetized rat and guinea pig is analyzed. In both animals, voiding is ch aracterized by an increase in intravesical pressure and then a decreas e, which is accompanied by flow through the urethra and emission of ur ine. An ultrasonic flow probe was used in both species to measure the flow rate in relation to the intravesical pressure. In the (male) rat, so-called high-frequency oscillations are superimposed on the decreas ing bladder pressure. These oscillations do not occur in the guinea pi g. It is concluded that the high-frequency oscillations are caused by intermittent flow and not by variations in the bladder contraction. Th e intermittent flow most likely is caused by the relaxation and contra ction of the external urethral sphincter and may have a function in te rritory marking. In our view, it is not likely that the oscillations e nhance bladder emptying, as has been suggested in the literature.